On-site Sewage Systems and Water Supply Wells: What to do Before, During, and After a Flood

What is a Flood?

“Flooding” can mean different things in different circumstances. Typically when we speak of flooding we think of a river that has overflowed its banks due to heavy rain or melted snow. Flooding can also simply mean a higher level of surface water than normal. The water levels of surface waters such as lakes, streams, or other water bodies typically fluctuate unless there are man-made water control structures in place. The water level in Lake Michigan, for example, typically fluctuates more than 12 inches in one year, and in October of 2018 the water level was more than six feet higher than the peak low recorded in the summer of 2012!

This page discusses the impact of high water levels on on-site water wells and sewage systems, whether the high levels are from periodic or seasonal fluctuations, or from specific precipitation-induced flooding events.. In either case, water levels that rise higher than the well casing or saturate the soils to a level within four feet of the bottom of a sewage system can be harmful to human health and the environment.

Under normal conditions, the top of the well head, and therefore the well casing vent, is at least 12 inches above the ground surface and is at least 24 inches above the maximum anticipated flood line. In a properly designed and functioning sewage treatment system, there is a minimum of four feet of unsaturated soil beneath the system allowing for an abundance of oxygen (O2) to treat the wastewater and reduce or eliminate harmful pathogens.If flood waters rise above the top of the well head, the well can become contaminated with flood water and all of the harmful contaminants floodwater contains. The well must then be disinfected by a well driller and water should not be consumed until lab tests have shown it is safe to drink. During flood events or times of elevated seasonal high water, saturated soil conditions beneath a sewage system can reduce or eliminate the oxygen (O2) present leading to inadequately treated sewage. Harmful pathogens can then be transported great distances and can even contaminate the drinking water well for your own home!

Before a Flood

Before a flood, be sure to:

Know where the parts of your sewage system and water supply are. BEDHD may have a drawing of the systems.

Perform routine maintenance so that you know the current status of your on-site systems.

Open wounds and rashes exposed to floodwater can become infected. Vibrios, for example, are naturally occurring bacteria that live in certain coastal waters and can cause skin infections when an open wound is exposed to them. This can happen during floods. To protect yourself and your family:

Avoid exposure to floodwater if you have an open wound.

Cover clean, open wounds with a waterproof bandage to reduce chance of infection.

Keep open wounds as clean as possible by washing well with soap and clean water.

Be aware that floodwater may contain sewage, and eating or drinking anything contaminated by floodwater can cause diarrheal disease (such as E. coli or Salmonella infection). To protect yourself and your family:

Wash your hands after contact with floodwater. Also be sure to wash children’s hands with soap and water often and always before meals.

Do not allow children to play in floodwater areas.

Do not allow children to play with toys that have been contaminated by floodwater and have not been disinfected.

Do not bathe in water that may be contaminated with sewage or toxic chemicals. This includes rivers, streams, or lakes that are contaminated by floodwater.

After a Flood

Do not pump the tank during flooded or saturated drainfield conditions.

At best, pumping the tank is only a temporary solution. Under worst conditions, pumping it out could cause the tank to try to float out of the ground and may damage the inlet and outlet pipes. The best solution is to plug all drains in the basement and drastically reduce or stop water use in the house.

Once floodwaters have receded, there are several things homeowners should remember:

Do not drink well water until it is tested. Contact BEDHD’s Environmental Health Division at (269) 945-9516 (Barry County) or (517) 541-2615 (Eaton County) with water sampling questions. If the floodwater has gone over the top of the well casing, the well should be disinfected prior to using it for drinking water.

Do not use the sewage system until water in the soil absorption field is lower than the water level around the house. A sewage system cannot properly treat pathogens unless the soil absorption system is sufficiently above the water table.

Have your septic tank professionally inspected and serviced if you suspect damage. Signs of damage include settling or an inability to accept water. Most septic tanks are not damaged by flooding since they are below ground and completely covered. However, septic tanks and pump chambers can fill with silt and debris, and must be professionally cleaned. If the soil absorption field is clogged with silt, a new system may have to be installed.

Only trained specialists should clean or repair septic tanks because tanks may contain dangerous gases. Contact BEDHD’s Environmental Health Division at (269) 945-9516 (Barry County) or (517) 541-2615 (Eaton County) for a list of septic system contractors who work in your area.

If sewage has backed up into the basement, clean the area and disinfect the floor. Use a chlorine solution of a half cup of chlorine bleach to each gallon of water to disinfect the area thoroughly. For more information, visit our page on home flooding safety.

Do not compact the soil over the soil absorption field by driving or operating equipment in the area. Saturated soil is especially susceptible to compaction, which can reduce the soil absorption field’s ability to treat wastewater and lead to system failure.

Examine all electrical connections for damage before restoring electricity.

Be sure the septic tank’s manhole cover is secure and that inspection ports have not been blocked or damaged.

Remember: Whenever the water table is high or your sewage system is threatened by flooding there is a risk that sewage will back up into your home. The only way to prevent this backup is to relieve pressure on the system by using it less.

Remember: Sewage is not being treated if the sewage system is flooded.

Here are some suggestions offered by experts for homeowners with flooded septic systems:

Use common sense. If possible, don’t use the system if the soil is saturated and flooded. The wastewater will not be treated and will become a source of pollution. Conserve water as much as possible while the system restores itself and the water table fails.

Prevent silt from entering septic systems that have pump chambers. When the pump chambers are flooded, silt has a tendency to settle in the chambers and will clog the drainfield if it is not removed.

Do not open the septic tank for pumping while the soil is still saturated. Mud and silt may enter the tank and end up in the drainfield. Furthermore, pumping out a tank that is in saturated soil may cause it to “pop out” of the ground. (Likewise, recently installed systems may “pop out” of the ground more readily than older systems because the soil has not had enough time to settle and compact.)

Do not dig into the tank or drainfield area while the soil is still wet or flooded. Try to avoid any work on or around the disposal field with heavy machinery while the soil is still wet. These activities will ruin the soil’s ability to accept wastewater.

Flooding of the septic tank will have lifted the floating crust of fats and grease in the septic tank. Some of this scum may have floated and/or partially plugged the outlet tee. If the septic system backs up into the house check the tank first for outlet blockage. Clean up any floodwater in the house without dumping it into the sink or toilet and allow enough time for the water to recede. Floodwaters from the house that are passed or pumped through the septic tank will cause higher flows through the system. This may cause solids to transfer from the septic tank to the drainfield and will cause clogging.

Locate any electrical or mechanical devices the system may have that could be flooded and avoid contact with them until they are dry and clean.

Aerobic plants, upflow filters, trickling filters, and other media filters have a tendency to clog due to mud and sediment. These systems will need to be washed and raked.